1. Field of the Invention
The present invention relates to a magnetic material which is particularly suited for use in low-current transmission engineering. This magnetic material has improved stability preventing transformation to the martensitic phase and a high initial permeability.
2. Summary of the Prior Art
Metallic materials which are characterized by an ease of magnetization, and which exhibit a high permeability at low field strength are particularly useful in low current transmission engineering. In particular, such materials find considerable use from the space saving standpoint for example, in transmitters, a high inductivity can be obtained employing a relatively small number of turns. Thus, the primary pre-requisite in communication engineering is for magnetic material to exhibit a high initial permeability.
In addition, these magnetic materials must also possess a high degree of stability so that the magnetic characteristics are stable over the temperature range of intended operation. Moreover, depending upon the mode of the functioning of the magnetic materials additional requirements must be met before the materials can be successfully employed. Commensurate in this regard, a high specific electrical resistance is needed in order to keep the eddy current loss component as small as possible, at the dimensions of the material employed.
The highest permeability alloys within the iron-nickel-molybedenum composition include from 70 to 80% nickel; however, these alloys are unsatisfactory from the eddy current standpoint. A further disadvantage of these materials as well as the other known high permeability alloys containing 45 to 65% nickel concerns the aspect that the most favorable permeability values are obtained only when the heat treatment processes carried out for this purpose are performed with the very greatest of care.
In addition to the foregoing two groups of materials, there are also known the binary nickel-iron alloys which contain 32 to 40% nickel, and more particularly 35 to 37% nickel. These alloys have a relatively high initial permeability, and in addition, they have a relatively very high specific resistance. This latter aspect is more clearly set forth in German Pat. No. 1,273,210, and Technical News Krupp, Research Report Volume 23, 1965, page 101; FIG. 8. Since these alloys were produced with sufficiently high purity, resulting from smelting in an extremely high vacuum, permeability values .mu..sub.5 of more than 20,000 Gauss/oersteds were obtained at a magnetic field of 5 mOe. Such binary nickel-iron alloys have not only the disadvantage that the necessary degree of purity can be obtained only at great expense, but in addition, such binary alloys are not stable and readily transform to martensite to any satisfactory degree. A comparison of the binary phase diagram of the iron-nickel alloy system can be found, for example, in the publication by E. Houdermont, Handbook of Special Steel Science, 3rd edition, 1956, at page 552. The 35% nickel-iron alloy undergoes the martensitic transformation of gamma to alpha at a temperature of -100.degree. C, a temperature which is nearly 100.degree. C above that of liquid nitrogen and which is above the temperatures often encountered in cryogenic applications of such material.